OP is asking about a non winch compatible bar, ie one without the opening for the cable or access to a winch.
His bar will need to be cut and likely add bracing to it.
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Yes, you can, it is quite easy if you know how to weld.
Use 40x5mm flat bar to brace the bar, add a strip across the bottom, where the vertical face is folded into the return at the bottom of the bar, and weld in two uprights to pick up the winch bolts and fairlead.
Alternatively install a cradle behind the bar, and just mount the fairlead to the bar.
There is a helluva lot of misinformation already in this thread, let those that have done it do the talking ;)